Recent multi-dimensional simulations suggest that high-entropy buoyant plumes help massive stars to explode^1,2. Outwardly protruding iron (Fe)-rich fingers of gas in the galactic supernova remnant^3,4 Cassiopeia A seem to match this picture. Detecting the signatures of specific elements synthesized in the high-entropy nuclear burning regime (that is, α-rich freeze out) would constitute strong substantiating evidence. Here we report observations of such elements—stable titanium (Ti) and chromium (Cr)—at a confidence level greater than 5 standard deviations in the shocked high-velocity Fe-rich ejecta of Cassiopeia A. We found that the observed Ti/Fe and Cr/Fe mass ratios require α-rich freeze out, providing evidence of the existence of the high-entropy ejecta plumes that boosted the shock wave at explosion. The metal composition of the plumes agrees well with predictions for strongly neutrino-processed proton-rich ejecta^2,5,6. These results support the operation of the convective supernova engine via neutrino heating in the supernova that produced Cassiopeia A.

最近的多维模拟表明，高熵浮力羽流有助于大质量恒星爆炸^1,2。银河超新星残骸中向外突出的富含铁 (Fe) 的气体指^3,4仙后座 A 似乎与这张照片相匹配。检测在高熵核燃烧状态（即富含 α 的冻结）中合成的特定元素的特征将构成强有力的证据。在这里，我们报告了在仙后座 A 受到冲击的高速富铁喷射物中以大于 5 个标准偏差的置信水平对稳定钛 (Ti) 和铬 (Cr) 的观察结果。我们发现观察到的 Ti/Fe和 Cr/Fe 质量比需要富含 α 的冻结，这提供了存在高熵喷射羽流的证据，这些喷射羽流在爆炸时增强了冲击波。羽流的金属成分与强中微子处理的富质子喷射物的预测非常吻合^2,5,6. 这些结果支持通过产生仙后座 A 的超新星中的中微子加热来运行对流超新星引擎。